The present invention relates to a particle optical apparatus, such as an ion implantation apparatus, an Auger electron spectrometer, an XPS analysis apparatus, and the like, with a radiation source by means of which a wafer or substrate brought into the apparatus can be bombarded by radiation providing for at least a positively charged surface layer of the wafer or substrate, the apparatus further comprising a charge neutralization device with means for providing secondary electron emission and transport means for transporting secondary electrons. In case of an ion implantation apparatus an ion source is present by means of which a wafer or substrate can be bombarded by positively charged particles. In case of an Auger electron spectrometer an electron source is present by means of which a wafer or substrate can be bombarded by electrons. In case of an XPS analysis apparatus an X-ray source is present by means of which a wafer or substrate can be bombarded by X-rays. In all these cases a charge neutralization device with means for providing secondary electron emission and transport means for transporting secondary electrons will be present.
A particle optical apparatus as described in the preamble is known from e.g. JPA-62.98548 and JP-A-03.25846.
The means for providing secondary electron emission comprises an electron source for generating primary electrons of relatively high energy, by means of which in a secondary electron generating box secondary electrons of relatively low energy are generated. Although in JP-A-62.98548 the secondary electron generating box is designed to prevent the primary electrons from directly reaching a wafer or substrate in the particle optical apparatus, a certain contamination of the secondary electrons with high energy primary electrons will always occur. Such a contamination can damage the wafer or substrate. For this reason it is often necessary to place the contaminated secondary electron source not too close to the wafer or substrate, which, however, leads to an insufficiently controlled implantation process.
The purpose of the invention is to obviate or at least to mitigate the above disadvantage and to provide for a particle optical apparatus in which the contamination of the secondary electrons with high energy primary electrons is further reduced.
According to the invention, the particle optical apparatus as described in the opening paragraph is characterized in that the charge neutralization device is provided with a hollow insulating structure for controlled electron transport based on secondary electron emission. Particularly the hollow insulating structure is an electron duct in vacuum with electrodes at the entrance and exit by means of which the necessary transport field in the duct is realized. Contamination originating from the primary electron source, mostly formed by a thermionic cathode and consisting of material that evaporates from the cathode, such as barium or tungsten, are absorbed in the electron duct, so that the exit thereof can be considered as a clean electron source. Furthermore, high energy primary electrons entering the electron duct loose most of their energy and will not reach the exit of the-duct, so that at the exit of the duct only secondary electrons are emitted. So, the exit of the duct cannot only be considered as a clean electron source but indeed as a clean secondary electron source. For these reasons and because the electron duct can be shaped in almost every form, the exit of the electron duct can be put into the vicinity of the location where a wafer or substrate can be brought into the apparatus without this secondary electron source causing any deterioration thereof. A secondary electron source in the vicinity of the wafer or substrate opens the possibility to flood the wafer or substrate with electrons having a reduced kinetic energy, thus practically preventing damaging the wafer or substrate.
The invention not only relates to a particle optical apparatus, but also to a charge neutralization device with a hollow insulating structure for controlled electron transport based on secondary electron emission for application in a particle optical apparatus as described above.
The invention, particularly the ion implantation apparatus, may be applied for the manufacture of semiconductors, SIMM""s (single-in-line memory modules), etc.